Fuel pressure???

[PRINCETON_JAKE]

My truck had a brand new lift pump, (the stock diafram type). I installed a fuel pressure gauge awhile back just for the heck of it. I hooked it up AFTER the fuel filter, and also installed BOTH the high flow banjo bolts. I was suprised that the highest the pressure ever was is 6 psi at idle, and even worse, the gauge dropped to zero psi, very fast if i got on it. So anyways i got the new low pressure piston style lift pump in today, at idle it peaks at 14 psi, if i put my foot to the floor, on a hard pull, the gauge drops to about 7 psi. Is that normal??? i thought the piston pumps had a higher volume, and hardly dropped at all.

My trucks pretty much stock, even stock injectors. The mods i have so far, 12 cm exhaust housing, big amsoil air filter right on turbo, injection pump turned ALL the way up, strait exhaust,

[Richie O]

I can pull mine to 3 psi.

[PToombs]

That's not bad pressure. I used to have 15 to 16 at idle, about 11 at WOT. I think I scarfed the innards some because the inlet screen was plugged and the pressure is down a little. You should run a prefilter or screen of some type. I'm upgrading to a 1/2" suction line and a full size prefilter with a glass bottom so I can see contaminants.

[lectro_static]

That's not bad pressure. I used to have 15 to 16 at idle, about 11 at WOT. I think I scarfed the innards some because the inlet screen was plugged and the pressure is down a little. You should run a prefilter or screen of some type. I'm upgrading to a 1/2" suction line and a full size prefilter with a glass bottom so I can see contaminants.

What size return line are you going to run? I am going to do 1/2" line suction line but am thinking it would benefit from a larger return line also.

[PToombs]

I'm going to use the stock one. It's 5/16", should be plenty for what I do. If it's not, then I'll mod that too. The line from the LPLP (low pressure lift pump) to the filter head is 5/16 too. I'm going to do some modding in the filter head, and take out the heater. I kinda forgot it was in there obstructing things.

[dpuckett]

Sounds like you have a restritcion somewhere upstream of the lift pump. Check the screen in the tank for clogging and such. With stock injectors and a near-runaway pump, I could only pull my piston pump down a few psi. Peak boost was ~25 or so, IIRC.

Dan

[Douglas]

hey-Hey!!!,
Could y'all tell me exactly which piston lift pump you have and where did it come from? Some further questions while I'm at it...since they ride on the cam, and likely have more pressure on their lifter. Does any special break-in need to happen? Rev-Lube on it? Any special mods to the fuel line hook-up?
cheers,
Douglas

[Richie O]

hey-Hey!!!,
Could y'all tell me exactly which piston lift pump you have and where did it come from? Some further questions while I'm at it...since they ride on the cam, and likely have more pressure on their lifter. Does any special break-in need to happen? Rev-Lube on it? Any special mods to the fuel line hook-up?
cheers,
Douglas

Look here
http://www.dieseltruckresource.com/dev/ ... 93722.html

[Douglas]

hey-Hey!!!,
Thanks for the link! very sweet. Just a note on it, the banjo seal rings; if they're made from Cu they can be re-anealed and re-used... In case one gets absent minded at the parts counter. Heat them red-hot and quench in water. I was stuck with that on my Merc 300 TDT all the time; hung them over a cup of water on a piece of coat hanger and heated with a MAP gas torch. When red, drag it off the hanger with a bent paperclip. If they're Aluminium, it is going to be get back to the parts man...heh-heh-heh.

I'll be taking the list to the good folks at Superior Turbo and Injection in Detroit shortly.
cheers,
Douglas

[ahale2772]

i think the low pressure pums really need a free flowing fuel system i installed one on a guys truck about a month a god and the truck has stock lines and just one turn on the fuel screw and he can pull it down to fourpsi pulling a trailer, i know with my high pressure pump and reg im getting upwards of 20psi and incrasing with rpm never had any problems with starvation, thats with 3/8s lines and i thing thats one of the reasons i can keep such a good flow

[PToombs]

The screen in his module may be plugged too. I couldn't pull mine below 10-11 with my 370's and the screw maxed until I got crap in mine.

[ahale2772]

pete where is the screen?

[PToombs]

Unscrew the big lock ring on the sender/pickup fuel module, and pull it out. There is one on the bottom, and 1 inside. Most of the time it sucks returned fuel thru the inner one, but when it's low it will suck thru the outer one. To get to the inside one pull the 3 screws, unsnap the fuel lines, and pull the bottom off the module. Don't forget the sender wires too. All you really need to do is look when it's out. You can see both screens with out pulling it apart.
There is a screen on the inlet of the piston LP too. Small stuff can go thru that though. I think that's what happened to mine. I still need to pull it and look.

[dpuckett]

Not to split hairs, but heating then quenching is hardening. Annealing is when you heat it, then stick it in some lime or wood ash to let it cool very slowly.

I had wondered about annealing Cu, and if it showed heat like steel or if it was like Al, and you just had to "know".

[PToombs]

Dan, I have to agree with Douglas on this one. Copper seal rings or head gaskets on my motorcycles I used to do the same thing. Red hot and drop it in water. Softens it right up. Thought it was pretty cool the 1st time I did it.